Recently, with the increasing demand of large-area applications in displays, flexible electronic devices and solar cells, it is required that opto-electronic devices are manufactured in large area by the composition of periodic sub-structures whose critical dimensions are preferred to be the smaller the better. It is predictable that there will be more and more manufacturers focusing their effort on submicron-scaled, or even nano-scaled periodic structures. However, to achieve such submicron-scaled, or nano-scaled periodic structures, it is important to have an alignment device capable of positioning in nano-scaled precision, which is especially true for trying to manufacture a large-area device with microstructures by a means of interference lithography as it requires multiple exposures and stitches. Therefore, it is crucial to have a stable alignment device capable of traveling in long stroke while positioning in nano-scaled precision.
There are already many studies relating to such effort. One of which is a method and system for interference lithography utilizing phase-locked scanning beams, disclosed in U.S. Pat. No. 6,882,477. The invention utilizes a high-precision stage that moves a substrate under overlapped and interfering pairs of coherent beams, and thus generates fringes, which form a pattern “brush” for subsequent writing of periodic patterns on the substrate, while altering the phases of the coherent beams by the use of an acousto-optic modulator (AOM) so as to enable the phase of the fringes in the overlapped region to be phase-locked, and thus produce periodic structures in large area with interference fringes of critical period and line width. As the phase-lock is ensured by the use of acousto-optic modulator (AOM), the aforesaid method is operational even under the influence of high-frequency external noises. In addition, as the positioning of the aforesaid patent is not performed by a mechanical mechanism, the platform for the aforesaid interference lithography method can enjoy a comparatively longer lifespan.
As the use of non-mechanical mechanism for aligning and positioning is common in prior arts, only a few efforts exist to develop a mechanism positioning device, especially in the field of interference lithography. Generally, any currently available positioning device either is capable of traveling in long stroke but with low positioning precision, or is capable of positioning with high precision but only in short stroke. Although following the progress of motor control technique and the advance of fabrication process for mechanical parts, those long-stroke, low-precision positioning device, represented by a device composed of motors and screw rods that is designed with a stroke of about 200 mm, can achieve micron-scaled or even submicron-scaled positioning accuracy, their precisions are still not good enough for manufacturing microstructures whose critical dimensions are smaller than submicron.
As for the short-stroke, high-precision positioning device being represented by a piezoelectric actuator, it utilizes the principle that the deformation of a piezoelectric material is in direct proportion with the voltage exerted thereon for driving a platform to move in response to the variation of the voltage. Moreover, if the piezoelectric actuator is controlled by a digital control device, the minimum displacement of the platform caused by the piezoelectric actuator is determined by the resolution of a digital-to-analog converter of the digital control device, i.e. the higher resolution the digital-to-analog converter are configured with, the more delicate response the piezoelectric material can be enabled to react. In addition, as the piezoelectric material can respond very fast to an applied voltage, it allows the piezoelectric actuator to have relatively high bandwidth. From the above description, it is concluded that the mobile platform which uses a piezoelectric material as actuator is suitable to be configured for compensating positioning error and also for suppressing the adverse affection of ambient vibrations working on the whole mobile platform system. However, such mobile platform of piezoelectric actuator is only capable of traveling in a very short stroke, which can be no more than 0.5 mm in general.
Please refer to FIG. 1A and FIG. 1B, which are schematic diagrams showing the alignment of two patterns of microstructures in two different manners. In FIG. 1A, the pattern 10, being formed on a workpiece 1 by lithography, is moved in a stepwise manner following a Y direction defined by a Cartesian coordinate system of X-axis and Y-axis so as to be aligned and thus stitched with another pattern 11 formed next to the pattern 10. As shown in FIG. 1A, the fringes within the ranges of the pattern 10 and pattern 11 are aligned parallel with the Y direction so that the two patterns can be aligned perfectly for stitching the two together. However, in most case, the fringes within the ranges of the two patterns are usually not aligned perfectly parallel along with their moving direction, as those shown in FIG. 1A, but are aligned as those shown in FIG. 1B, especially when the patterns are nano-scaled patterns. In FIG. 1B, the fringes in the pattern 12 are deflected from the Y direction by a specific angle, which is caused by the positioning error of the interference beams during calibration. Thereby, as another pattern 13 is formed next to the pattern 12 at a side thereof, the fringes will not be aligned perfectly and thus there are positioning error between adjacent interference patterns 12, 13 during step-and-align interference lithography.